1. Field of the Invention
The present invention relates to a fixing apparatus applied to image forming apparatuses such as a copying machine and a printer, particularly to an apparatus for applying a fixing member with a releasing agent.
2. Related Background Art
FIG. 10 shows a fixing apparatus as a background art of the present invention.
As shown in detail in FIG. 10, the fixing apparatus is constituted of a fixing roller 510 as a fixing rotating member which is rotatably disposed, a pressurizing roller 520 as a pressurizing rotating member which is pressed in contact with the fixing roller 510 and rotates, a releasing agent applying apparatus 530 as releasing agent applying means, cleaning apparatuses 540, 550, and the like. Additionally, heaters 560, 570 such as halogen lamps are disposed inside the fixing roller 510 and pressurizing roller 520, respectively. Moreover, thermistors 580, 590 are disposed to abut on the fixing roller 510 and pressurizing roller 520, respectively, and surface temperatures of the fixing roller 510 and pressurizing roller 520 are adjusted by controlling voltages to the heaters 560, 570 via a temperature adjustment circuit.
The releasing agent applying apparatus 530 is constituted of: a releasing agent reservoir 530a for containing releasing agents such as silicone oil; pumping rollers 530b, 530c for pumping the releasing agent from the releasing agent reservoir 530a; an applying roller 530d for applying the pumped releasing agent to the fixing roller 510; a regulating blade 530e, formed of elastic materials such as fluorine rubber, for regulating a releasing agent amount on the applying roller 530d to provide a constant amount; and the like. Particularly to realize uniform applying of the fixing roller 510 with the releasing agent, the releasing agent applying apparatus 530 is disposed on the downstream side of the rotation direction of the fixing roller 510 with respect to the thermistor 580.
Therefore, when a recording sheet P is conveyed, the fixing roller 510 and pressurizing roller 520 rotate, and the surface of the fixing roller 510 is applied with silicone oil as the releasing agent. When the recording sheet P passes between the fixing roller 510 and the pressurizing roller 520, the recording sheet is pressurized and heated with substantially constant pressure and temperature from both front and back surfaces, an unfixed toner image is fixed and an image is formed on the recording sheet P. Moreover, the recording sheet P with the image fixed thereto is separated from the pressurizing roller 520 by a lower separating pawl 680 and discharged to the outside.
However, this apparatus has the following problem.
Namely, the general thermal fixing apparatus in a copying machine or the like is on standby for a predetermined time after power is turned on until the fixing roller reaches a predetermined temperature, and a copy enable state is obtained after the fixing roller reaches the predetermined temperature. Fixing properties differ immediately after the copy enable state is obtained (hereinafter referred to as xe2x80x9cstate of first run in the morningxe2x80x9d), and when the apparatus is left on standby in the copy enable state and a predetermined time elapses (hereinafter referred to as xe2x80x9cleft statexe2x80x9d). This is because not only the surface temperature of the fixing roller but also the temperature of the entire fixing apparatus and particularly the temperature of the releasing agent applied to the fixing roller surface differ with the state of first run in the morning and the left state. Namely, in the left state, since fixing roller heat is conducted to the releasing agent via the applying roller and pumping roller, the releasing agent gains a high temperature. In this state, even when the releasing agent is applied to the fixing roller, the fixing roller indicates a little temperature drop.
Additionally, since the releasing agent present between the fixing roller and toner also has a high temperature, the fixing property is enhanced.
On the other hand, in the state of first run in the morning, the temperature of the releasing agent is low. When the low-temperature releasing agent is applied to the fixing roller surface, the temperature of the fixing roller rapidly lowers. Additionally, since the low-temperature releasing agent exists between the fixing roller and toner surface, the fixing property is deteriorated. This is further remarkable in a low temperature environment.
An object of the present invention is to provide a fixing apparatus which performs satisfactory fixing irrespective of temperature of a releasing agent.
Another object of the present invention is to provide a fixing apparatus comprising: a fixing member for fixing an unfixed image onto a recording material; releasing agent applying means for applying a releasing agent to the fixing member; temperature detecting means for detecting temperature of the releasing agent; and control means for controlling a fixing condition in accordance with a detected temperature from the temperature detecting means.
Further objects of the present invention will be apparent in the following description.